1. Field of the Invention
The present invention relates to a new and improved coupling and more particularly to a brake assembly having first and second torque transmitting members wherein a flow of cooling fluid is directed to cool one side of the first torque transmitting member and a flow of lubricant is directed to the engageable surfaces of the first and second torque transmitting members to provide for a mixed boundary contact therebetween.
2. Background of the Invention
Many known couplings are provided which utilize a fluid for cooling the torque transmitting element of the coupling. For example, the Sanford et al U.S. Pat. No. 2,889,897, discloses a liquid cooled brake wherein fluid flow is directed sequentially through the brake to effect cooling thereof and through a heat exchanger to cool the cooling fluid. Peermain et al, U.S. Pat. No. 1,978,687, discloses a clutch provided with cooling passageways therein and Hanks, U.S. Pat. No. 3,667,581, discloses a combination clutch brake having air cooling passageways disposed therein. Additionally, Heaney, U.S. Pat. No. 1,248,109, discloses a cone clutch brake in which the friction surfaces are bathed in lubricant. None of the prior art discloses a coupling wherein there is simultaneously provided fluid cooling of one side of the coupling surfaces along with oil lubrication of the mating side thereof to provide a mixed boundary contact between the coupling members. The art seems to teach that if you use oil lubrication for a coupling then there is no need for water cooling as the lubricating oil also acts as a cooling fluid. However, it has been found that the simultaneous use of a cooling fluid with oil lubrication effectively cools the coupling and the lubricating fluid, making the lubricating fluid a more effective lubricant due to the lower operating temperature.
The use of water as a cooling medium in an oil lubricated coupling provides the same advantages of a normal oil lubricated coupling but with far greater heat dissipating capabilities. Water has a higher film coefficient than oil and a higher specific heat and therefore absorbs heat better than oil and acts as a better heat transfer medium. For example, a 20 H.P. coupling needs an oil flow therethrough of 8 gal./min. with about a 30 gallon reservoir while the same size coupling cooled with water needs only about a 2 gal./min. flow. Thus, the water cooled oil lubricated coupling can be used with a much lower fluid flow therethrough when water is being used as a cooling medium. Since a relatively small flow of water is needed for cooling, there is no need to recirculate the water as one would recirculate the oil if it were used for cooling. Additionally, since the water is not recirculated, there is no need for a heat exchanger as is used in an oil cooled coupling where the heat exchanger is used to cool the recirculated oil. The use of a heat exchanger to cool the oil is inefficient as the heat is first transferred to the oil from the coupling and then from the oil through the heat exchanger to either air or water which is used to cool the heat exchanger. In Applicant's invention the heat is transferred more efficiently from the coupling directly to water.
The utilization of Applicant's structure provides a completely enclosed coupling having high torque and energy capacity wherein water cooling of the coupling members occurs. Since the cooling water is separated from the coupling surfaces and lubricant flow, it does not become contaminated. Since the cooling fluid does not become contaminated, the need for a closed recirculation system can be eliminated as regular tap water can be continuously circulated throughout the cooling passageways of the coupling and then directed to drain. Also, since the lubricant is cooled by the cooling fluid, there is no need for a heat exchanger to cool the lubricating fluid.